Lead frame

ABSTRACT

A lead frame includes a die pad, a suspension lead and a plurality of leads. The group of leads include at least three kinds of leads, including first, second and third leads. While the first lead and the third lead are connected to each other upon production of the lead frame, a connecting portion therebetween has a smaller thickness than that of the frame body so that the first lead and the third lead can be separated from each other in a subsequent step.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a lead frame for use in a landgrid array (LGA) type resin-encapsulated semiconductor device.

[0002] In recent years, a resin-encapsulated semiconductor device of atype called “QFN” (quad flat non-leaded package) has been developed inthe art, in which an encapsulation resin is provided substantially onlyon the upper side of a lead frame (i.e., the lead frame is molded on oneside), in an attempt to realize a small and thin resin-encapsulatedsemiconductor device. A conventional QFN type resin-encapsulatedsemiconductor device in which a die pad is exposed on the reversesurface of the package will now be described.

[0003]FIG. 11 is a cross-sectional view illustrating a conventional QFNtype resin-encapsulated semiconductor device. FIG. 12 is a plan viewillustrating a lead frame used in the conventional QFN typeresin-encapsulated semiconductor device. As illustrated in FIG. 12, thelead frame used in the conventional resin-encapsulated semiconductordevice includes an outer frame 107, or a frame body, having an openingtherein, a rectangular die pad 101 placed substantially in the center ofthe opening, suspension leads 108 each having one end connected to acorner of the die pad 101 and the other end connected to the outer frame107 for supporting the die pad 101, and a plurality of inner leads 103each extending toward the corresponding side of the die pad 101. Theconventional QFN type resin-encapsulated semiconductor device (package)includes the die pad 101, the suspension leads 108 and the inner leads103 of the lead frame, a semiconductor chip 102 bonded on the die pad101 of the lead frame, thin metal wires 104 electrically connectingelectrodes of the semiconductor chip 102 with some of the inner leads103, and an encapsulation resin 105 encapsulating the semiconductor chip102, the inner leads 103, the thin metal wires 104, the suspension leads108 and the die pad 101 together on the upper side of the lead frame.Note however that the reverse surface of the die pad 101, and thereverse surface and the outer side surface of each inner lead 103 arenot covered with the encapsulation resin 105 but are exposed on thereverse surface or the side surface of the package. The reverse surfaceportion and the outer side surface portion of each inner lead 103function as an external terminal 106.

[0004] Note that although FIG. 12 only shows, as a unit, a region of thelead frame on which one semiconductor chip is mounted, the entire leadframe actually includes a plurality of such units as illustrated in FIG.12 that are arranged next to each other in a matrix pattern.

[0005] Next, a method for manufacturing the conventional QFN typeresin-encapsulated semiconductor device will be described. FIG. 13A toFIG. 13D are cross-sectional views taken along line XIII-XIII of FIG.12, illustrating the method for manufacturing the conventionalresin-encapsulated semiconductor device.

[0006] First, in the step of FIG. 13A, a lead frame as illustrated inFIG. 12 is prepared, including the die pad 101 on which thesemiconductor chip is mounted, suspension leads (not shown) forsupporting the die pad 101, and the inner leads 103 each extendingtoward the corresponding side of the die pad 101 (see FIG. 11).

[0007] Next, in the step of FIG. 13B, the reverse surface of thesemiconductor chip 102 is bonded on the upper surface of the die pad 101via an adhesive, and the semiconductor chip 102 is mounted on the diepad 101 of the lead frame.

[0008] Next, in the step of FIG. 13C, the semiconductor chip 102 and abonding region of the upper surface of each inner lead 103 areelectrically connected to each other via the thin metal wire 104.

[0009] Then, in the step of FIG. 13D, the lead frame having a number ofsemiconductor chips mounted thereon is set in an encapsulation mold set,with a sheet material (not shown) being closely held on an upper mold ora lower mold of the encapsulation mold set, and a resin encapsulationprocess is performed, whereby the semiconductor chip 102, the innerleads 103, the thin metal wires 104, the suspension leads 108 and thedie pad 101 are encapsulated in the encapsulation resin 105 on the upperside of the lead frame. At this time, the reverse surfaces of the diepad 101 and each inner lead 103 are exposed, i.e., not covered with theencapsulation resin 105. Then, the lead frame is cut along the sidesurface of the encapsulation resin 105 so as to be divided intoindividual packages. In each package (resin-encapsulated semiconductordevice), the reverse surface portion and the outer side surface portionof each inner lead 103 function as an external terminal 106.

[0010] Although the above-described conventional QFN typeresin-encapsulated semiconductor device has an innovative structure as asmall and thin semiconductor device, there is much to be improved inorder to accommodate a further increase in the number of pins of asemiconductor chip to be mounted and a further reduction in size. Inview of this, an LGA type resin-encapsulated semiconductor device hasbeen recently proposed in the art, in which external terminals areprovided in two rows on the reverse surface of a package, in order tofurther reduce the size of the device and to increase the number ofexternal terminals.

[0011]FIG. 14A to FIG. 14C are an top view, a bottom view and across-sectional view taken along line XIVc-XIVc, respectively, eachillustrating an LGA type resin-encapsulated semiconductor deviceproposed in the prior art. FIG. 15 is a plan view illustrating a leadframe used in the LGA type resin-encapsulated semiconductor device. Asillustrated in FIG. 15, the lead frame used in the conventionalresin-encapsulated semiconductor device includes an outer frame 107, ora frame body, having an opening therein, a rectangular die pad 101placed substantially in the center of the opening, suspension leads 108each having one end connected to a corner of the die pad 101 and theother end connected to the outer frame 107 for supporting the die pad101, a plurality of first inner leads 103 a each extending toward thecorresponding side of the die pad 101, and a plurality of second innerleads 103 b each extending to a position closer to the die pad 101 thanthe first inner leads 103 a.

[0012] As illustrated in FIG. 14A to FIG. 14C, the LGA typeresin-encapsulated semiconductor device (package) includes asemiconductor chip 102 bonded on the die pad 101, the first and secondinner leads 103 a and 103 b, thin metal wires 104 electricallyconnecting the semiconductor chip 102 with the first and second innerleads 103 a and 103 b, and an encapsulation resin 105 encapsulating thesemiconductor chip 102, the inner leads 103 a and 103 b, the thin metalwires 104, the suspension leads (not shown) and the die pad 101 togetheron the upper side of the lead frame. Note however that the reversesurface of the die pad 101, the outer side surface and the reversesurface of each first inner lead 103 a, the outer side surface of eachsecond inner lead 103 b, and the reverse surface of the tip portion ofeach second inner lead 103 b are not covered with the encapsulationresin 105 but are exposed on the side surface or the reverse surface ofthe package. The reverse surface and the outer side surface of eachfirst inner lead 103 a, which are exposed respectively on the reversesurface and the side surface of the package, function as a firstexternal terminal 106 a. The reverse surface of each second inner lead103 b, which is exposed on the reverse surface of the package at aposition closer to the die pad 101 than the first external terminal 106a, functions as a second external terminal 106 b. Note that a lowerportion of each second inner lead 103 b is removed through ahalf-etching process except for the tip portion thereof, so that thesecond inner lead 103 b has a reduced thickness in the half-etchedportion.

[0013] Note that although FIG. 15 only shows, as a unit, a region of thelead frame on which one semiconductor chip is mounted, the entire leadframe actually includes a plurality of such units as illustrated in FIG.15 that are arranged next to each other in a matrix pattern.

[0014] Next, a method for manufacturing the conventional LGA typeresin-encapsulated semiconductor device will be described. FIG. 16A toFIG. 16D are cross-sectional views taken along line XVI-XVI of FIG. 15,illustrating the method for manufacturing the resin-encapsulatedsemiconductor device.

[0015] First, in the step of FIG. 16A, a lead frame is prepared,including the die pad 101 on which the semiconductor chip is mounted,the first inner leads 103 a each extending toward the corresponding sideof the die pad 101, and the second inner leads 103 b each extending to aposition closer to the die pad 101 than the first inner leads 103 a (seeFIG. 15).

[0016] Next, in the step of FIG. 16B, the semiconductor chip 102 isbonded and mounted on the die pad 101 of the lead frame via an adhesive.

[0017] Next, in the step of FIG. 16C, the semiconductor chip 102 and abonding region of the upper surface of each of the first and secondinner leads 103 a and 103 b are electrically connected to each other viathe thin metal wire 104.

[0018] Then, in the step of FIG. 16D, the lead frame having a number ofsemiconductor chips mounted thereon is set in an encapsulation mold set,with a sheet material (not shown) being closely held on an upper mold ora lower mold of the encapsulation mold set, and a resin encapsulationprocess is performed, whereby the semiconductor chip 102, the innerleads 103 a and 103 b, the thin metal wires 104, the suspension leads108 and the die pad 101 are encapsulated in the encapsulation resin 105on the upper side of the lead frame. At this time, the reverse surfaceof the die pad 101, the reverse surface and the outer side surface ofeach first inner lead 103 a, the reverse surface of the tip portion ofeach second inner lead 103 b, and the outer side surface of each secondinner lead 103 b are exposed, i.e., not covered with the encapsulationresin 105. Then, the lead frame is cut along the side surface of theencapsulation resin 105 so as to be divided into individual packages. Ineach package (resin-encapsulated semiconductor device), the reversesurface portion and the outer side surface portion of each first innerlead 103 a function as the first external terminal 106 a. The reversesurface portion of the tip portion of each second inner lead 103 b,which is at a position closer to the die pad 101 than the first externalterminal 106 a, functions as the second external terminal 106 b.

[0019] Although the above-described conventional QFN typeresin-encapsulated semiconductor device has a reduced size and a reducedthickness, it has not been sufficient for accommodating a furtherincrease in the number of pins. While the above-described conventionalLGA type resin-encapsulated semiconductor device accommodates anincreased number of pins and has two rows of external terminals, thereis a demand for such devices with more than two rows of externalterminals. LGA type resin-encapsulated semiconductor devices havingthree or more rows of external terminals have encountered other problemscaused by the increased number of rows of external terminals.

[0020] In order to increase the efficiency of the manufacturing process,an LGA type resin-encapsulated semiconductor device having three or morerows of external terminals is manufactured by the following process, forexample. That is, a plurality of units each including a chip mountedthereon are provided in a single lead frame, and the entire surface ofthe lead frame is resin-encapsulated at once by using an encapsulationresin such as an epoxy resin, after which the encapsulated lead frame iscut by a rotating blade such as a dicer into individual packages(resin-encapsulated semiconductor devices) each including a chip. In thestep of dividing the lead frame, which has been resin-encapsulated atonce, into pieces by using the rotating blade, stripping may occur atthe interface between the leads and the encapsulation resin, thuslowering the reliability of the product. Even after the encapsulatedlead frame is divided into individual packages (resin-encapsulatedsemiconductor devices) by using the rotating blade, stripping may occurat the interface between the leads and the encapsulation resin when astress is applied to a resin-encapsulated semiconductor device, thuslowering the reliability of the product.

SUMMARY OF THE INVENTION

[0021] An object of the present invention is to provide a lead frameused for producing a resin-encapsulated semiconductor device havingthree or more rows of lands (external terminals) on the reverse side ofthe resin-encapsulated semiconductor device.

[0022] A lead frame of the present invention includes: a frame body madeof a conductive material and including at least one opening for mountinga semiconductor chip; a die pad placed in the opening of the frame body;and a group of leads extending from the frame body into the opening. Thegroup of leads include at least: a first lead connected to the framebody and including a first bonding pad provided on an upper surface ofthe first lead and a first land provided on a lower surface of the firstlead; a second lead connected to the frame body and including a secondbonding pad provided on an upper surface of the second lead and a secondland provided on a lower surface of the second lead; and a third leadconnected to the first lead and including a third bonding pad providedon an upper surface of the third lead and a third land provided on alower surface of the third lead. A connecting portion that is thinnerthan the lead frame body and that can be punched through is providedbetween the first lead and the third lead.

[0023] In this way, upon production of the lead frame, the third lead isconnected to the frame body and is supported by the frame body. Then,the connecting portion is punched through in a subsequent step, wherebythe first lead and the third lead can be used while being electricallyseparated from each other. Therefore, a large number of lands, i.e., thefirst, second and third lands, can be used as external terminals withoutincreasing the number of leads that are connected to the periphery ofthe opening. Thus, it is possible to obtain a lead frame useful forproducing a semiconductor device having three or more rows of externalterminals.

[0024] At least the second lead may include a neck portion having asmaller width than other portions as viewed in a plan view. In this way,when the first, second and third leads are incorporated in aresin-encapsulated semiconductor device, the leads and the encapsulationresin contact each other over an increased contact area at the neckportion, whereby even if stripping occurs between the leads and theencapsulation resin, the progress of the stripping can be suppressed.

[0025] Each lead may include a region around the bonding pad thereofthat has a smaller thickness than that of a portion of the leadcorresponding to the bonding pad, with a stepped portion being providedbetween the bonding pad and the region around the bonding pad. Also inthis way, the progress of the stripping between the leads and theencapsulation resin can be suppressed.

[0026] The first, second and third lands may be substantially coplanaron a common plane while being arranged in three rows on the commonplane.

[0027] It is preferred that the second lead and a lead structureincluding the first and third leads are arranged alternately along aperiphery of the opening of the frame body.

[0028] It is preferred that the frame body, the die pad and the group ofleads are made of a single metal plate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a plan view illustrating a lead frame according to anembodiment of the present invention.

[0030]FIG. 2 is a cross-sectional view illustrating the same taken aloneline II-II of FIG. 1.

[0031]FIG. 3A and FIG. 3B are a plan view and a cross-sectional viewtaken along line IIIb-IIIb, respectively, illustrating a main portion ofthe lead frame according to an embodiment of the present invention.

[0032]FIG. 4A, FIG. 4B and FIG. 4C are a top view, a cross-sectionalview taken along line IV-IV and a bottom view, respectively,illustrating a resin-encapsulated semiconductor device according to anembodiment of the present invention.

[0033]FIG. 5A and FIG. 5B are a plan view and a cross-sectional viewtaken along line V-V, respectively, illustrating the step of preparing alead frame according to an embodiment of the present invention.

[0034]FIG. 6A and FIG. 6B are a plan view and a cross-sectional viewtaken along line VI-VI, respectively, illustrating the step of cutting aconnecting portion between a first lead and a third lead according to anembodiment of the present invention.

[0035]FIG. 7A and FIG. 7B are a plan view and a cross-sectional viewtaken along line VII-VII, respectively, illustrating the die bondingstep according to an embodiment of the present invention.

[0036]FIG. 8A and FIG. 8B are a plan view and a cross-sectional viewtaken along line VIII-VIII, respectively, illustrating the wire bondingstep according to an embodiment of the present invention.

[0037]FIG. 9A and FIG. 9B are a plan view and a cross-sectional viewtaken along line IX-IX, respectively, illustrating the resinencapsulation step according to an embodiment of the present invention.

[0038]FIG. 10A and FIG. 10B are a plan view and a cross-sectional viewtaken along line X-X, respectively, illustrating the dicing stepaccording to an embodiment of the present invention.

[0039]FIG. 11 is a cross-sectional view illustrating a conventional QFNtype resin-encapsulated semiconductor device.

[0040]FIG. 12 is a plan view illustrating a lead frame used in aconventional QFN type resin-encapsulated semiconductor device

[0041]FIGS. 13A, 13B, 13C and 13D are cross-sectional views taken alongline XIII-XIII of FIG. 12, illustrating a process of manufacturing aconventional QFN type resin-encapsulated semiconductor device.

[0042]FIGS. 14A, 14B and 14C are a top view, a bottom view and across-sectional view taken along line XIVc-XIVc, respectively,illustrating a conventional LGA type resin-encapsulated semiconductordevice.

[0043]FIG. 15 is a plan view illustrating a lead frame used in aconventional LGA type resin-encapsulated semiconductor device.

[0044]FIGS. 16A, 16B, 16C and 16D are cross-sectional views taken alongline XVI-XVI of FIG. 15, illustrating a process of manufacturing aconventional LGA type resin-encapsulated semiconductor device.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0045] A lead frame, a resin-encapsulated semiconductor device using thesame, and a method for manufacturing the same, according to anembodiment of the present invention will now be described with referenceto the drawings.

[0046] Lead Frame

[0047] First, a lead frame according to an embodiment of the presentinvention will be described.

[0048]FIG. 1 is a plan view illustrating a lead frame according to theembodiment of the present invention. FIG. 2 is a cross-sectional viewtaken along line II-II of FIG. 1. FIGS. 3A and 3B are a plan view and across-sectional view taken along line IIIb-IIIb, respectively,illustrating a main portion of the lead frame of the present embodiment.

[0049] As illustrated in FIG. 1, the lead frame of the presentembodiment includes a frame body 11 (outer frame) made of a metal platethat contains copper (Cu) as its main component. The frame body 11includes a number of openings in each of which a semiconductor chip isprovided. FIG. 1 shows only a portion of the lead frame corresponding toone opening, for the sake of simplicity. The lead frame includes, ineach opening, a die pad 12 on which a semiconductor chip is mounted,suspension leads 13 each having one end supporting a corner of the diepad 12 and the other end connected to the frame body 11, and a group ofleads each having a tip portion extending toward the corresponding sideof the die pad 12 and a base portion connected to the frame body 11. Theframe body 11, the die pad 12, the suspension leads 13 and the group ofleads are produced from a single metal plate.

[0050] The group of leads include at least three kinds of leads, i.e.,first, second and third leads 14, 15 and 16. A first bonding pad 14 a isprovided on the upper surface of each first lead 14, and a first land 14b, opposing the first bonding pad 14 a, is provided on the lower surfaceof the first lead 14. A second bonding pad 15 a is provided on the uppersurface of each second lead 15, and a second land 15 b, opposing thesecond bonding pad 15 a, is provided on the lower surface of the secondlead 15. A third bonding pad 16 a is provided on the upper surface ofeach third lead 16, and a third land 16 b, opposing the third bondingpad 16 a, is provided on the lower surface of the third lead 16.

[0051] Moreover, a region of each of the leads 14, 15 and 16 excludingthe bonding pads 14 a, 15 a and 16 a and the lands 14 b, 15 b and 16 bis a pressed region Rpres whose thickness is reduced through a pressingprocess as illustrated in FIG. 2. The bonding pads 14 a, 15 a and 16 arespectively include stepped portions 14 c, 15 c and 16 c protrudingupwardly from the press regions Rpres having a reduced thickness. Thelands 14 b, 15 b and 16 b, as viewed in a plan view on the lower surfaceof the lead frame, are arrayed in three rows as will be described later,and the lands 14 b, 15 b and 16 b function as external terminals when aresin-encapsulated semiconductor device (package) is produced.

[0052] The thickness t0 (see FIG. 2) of the frame body 11 is about 150μm to about 200 μm, for example, and the thickness of each of the leads14, 15 and 16 from the upper surface of the bonding pad to the lowersurface of the land is also t0. The thickness t1 (see FIG. 2) of thepressed region Rpres of each of the leads 14, 15 and 16, i.e., theregion excluding the bonding pad and the land, is about 80 μm to about120 μm, for example, the height h1 by which each of the bonding pads 14a, 15 a and 16 a protrudes from the pressed region Rpres is about 5 μmto about 50 μm, for example, and the height h2 by which each of thelands 14 b, 15 b and 16 b protrudes from the pressed region Rpres isabout 50 μm to about 120 μm, for example.

[0053] A first feature of the present embodiment is that while the firstlead 14 and the third lead 16 are connected to each other uponproduction of the lead frame, the thickness of the connecting portionRcnct therebetween is smaller than the thickness of the frame body 11 sothat the first lead 14 and the third lead 16 can be separated from eachother in a subsequent step. The thickness of the connecting portionRcnct between the first lead 14 and the third lead 16 is about 70 μm,for example, and the width thereof is about 100 μm, for example. Aportion of the connecting portion Rcnct indicated by a dotted line inFIG. 1 is punched through in a subsequent step so as to electricallyseparate the first lead 14 and the third lead 16 from each other.

[0054] In the lead frame of the present embodiment, the first lead 14and the third lead 16 can be separated from each other in a step afterattachment of the lead frame to an encapsulation sheet and before diebonding or wire bonding is performed, or in a step after the attachmentof the lead frame to the encapsulation sheet (following the die bondingor wire bonding) and before the resin encapsulation step. Thus, thefirst lead 14 and the third lead 16 are separated from each other in asubsequent step. In this way, it is possible to increase the number oflands to be external terminals without increasing the number of leadsthat are connected to the periphery of the opening of the frame body 11,whereby it is possible to obtain a lead frame that is advantageous inthe production of a resin-encapsulated semiconductor device having threeor more rows of external terminals.

[0055] In a case where the first lead 14 and the third lead 16 areseparated from each other by a process of punching through theconnecting portion Rcnct therebetween using a punch while the lead frameis attached to the encapsulation sheet, the connecting portion Rcnctneeds to be punched through with a punching force such that the entirelead frame is not stripped from the encapsulation sheet. In a case wheresuch a process is employed and the main component of the lead frame iscopper as in the present embodiment, it is preferred that the width ofthe connecting portion Rcnct is in the range of 40 μm to 100 μm, and thethickness thereof is in the range of 80 μm to 120 μm.

[0056] Moreover, a second feature of the present embodiment is that thesecond lead 15 includes a neck portion 17 that has a reduced width inthe vicinity of the second land 15 b. The width of the neck portion 17is about 40 μm to about 100 μm, for example.

[0057] Furthermore, although not shown, a reinforced land having alarger area than other lands (functioning as external terminals) isprovided in the vicinity of the base end of each suspension lead 13.Therefore, after the resin-encapsulated semiconductor device is producedthrough the resin encapsulation step, a reinforced land is exposed onthe reverse surface of the device at each corner thereof, therebyrealizing a structure with an increased secondary mounting reliability,i.e., the reliability of the device when it is mounted on a motherboard.

[0058] Moreover, a protruding portion 19 that is protruding from theother portions is provided in a central portion of the die pad 12 by apress, or the like, so that a semiconductor chip is mounted on theprotruding portion 19.

[0059] Moreover, since the die pad 12 includes the protruding portion 19that is protruding upwardly in the area of the upper surface thereof,when a semiconductor chip is mounted, the semiconductor chip will besupported by a spot-float structure. Since the semiconductor chip islifted up, external terminals can also be provided below thesemiconductor chip. Moreover, in the resin encapsulation step, theencapsulation resin can be placed between the reverse surface of thesemiconductor chip and the die pad 12 or below the protruding portion19, thereby further increasing the reliability.

[0060] Furthermore, a metal plating layer is formed across the entiresurface of the lead frame of the present embodiment. The lead frame ofthe present embodiment includes a base body whose main component iscopper (Cu) and a triple metal plating layer provided on the base body.The metal plating layer includes a nickel (Ni) layer, a palladium (Pd)layer and a gold (Au) layer.

[0061] The leads on which the plating layer has been formed aresubjected to a pressing process so as to form the stepped portions 14 c,15 c and 16 c on the bonding pads. After the pressing process, thecomposition of the plating layer in the pressed region Rpres around thearea defined by each of the stepped portions 14 c, 15 c and 16 c isdifferent from that of the region inside the area defined by each of thestepped portions 14 c, 15 c and 16 c (including the bonding pads 14 a,15 a and 16 a) because different portions receive different pressingforces from the pressing process. Particularly, an outermost surfaceportion may have a reduced proportion of the gold layer, which has agood adherence to the encapsulation resin, and an increased proportionof the palladium layer and the nickel layer, which have a poor adherenceto the encapsulation resin. Moreover, as the leads are subjected to apressing process, the irregularities on the surface of the plating layermay be eliminated in the pressed portions, thereby deteriorating theadherence. However, if the stepped portions 14 c, 15 c and 16 c areformed by pressing only the pressed region Rpres around the bonding pads14 a, 15 a and 16 a, the pressing force is not applied in the regioninside the area defined by each of the stepped portions 14 c, 15 c and16 c, and thus the composition of the plating layer does not change inthe area, whereby it is possible to maintain a resin adherence that theplating layer originally has. Therefore, even if stripping occurs at theinterface between the encapsulation resin and the leads, and proceeds tothe stepped portions 14 c, 15 c and 16 c, the stripping can be stoppedbefore it reaches the region inside the area defined by each of thestepped portions 14 c, 15 c and 16 c.

[0062] Specifically, when the stepped portions 14 c to 16 c are formedby pressing the leads 14 to 16, the pressing process is performed byusing a press die having a cavity corresponding to each region insidethe area defined by each of the stepped portions 14 c to 16 c of theleads 14 to 16 so that only the region around the bonding pads 14 a to16 a of the leads 14 to 16 is pressed while the pressing force is notapplied on the region inside the area defined by each of the steppedportions 14 c to 16 c (including the bonding pads 14 a to 16 a). In thisway, only the region around the bonding pads 14 a to 16 a of the leads14 to 16 can be pressed, whereby the resin adherence of the bonding pads14 a to 16 a can be maintained.

[0063] Thus, the bonding pads 14 a to 16 a of the leads 14 to 16 of thelead frame of the present embodiment are protruding from the pressedregion Rpres around the bonding pads 14 a to 16 a whose thickness hasbeen reduced through the pressing process, with the stepped portions 14c to 16 c being formed between the bonding pads 14 a to 16 a and thepressed region Rpres. Therefore, the bonding pads 14 a to 16 a have aresin adherence that the plating layer originally has.

[0064] While the metal plating layer of the lead frame of the presentembodiment has a multilayer structure including a nickel (Ni) layer, apalladium (Pd) layer and a gold (Au) layer, the metal plating layer mayalternatively be a single metal plating layer such as a silver platinglayer, a gold plating layer, or a solder plating layer.

[0065] By plating the lead frame before the pressing process as in thepresent embodiment, there is an advantage that the flow condition of theplating solution is more uniform across the lead frame surface, ascompared with a case where the lead frame is plated after the pressingprocess.

[0066] Moreover, as illustrated in FIG. 3B, the first lead 14, thesecond lead 15 and the third lead 16 have a tapered cross section, withthe lower surface (reverse surface) of the bonding pad being exposed onthe encapsulation resin surface to function as an external terminalafter the resin encapsulation step.

[0067] Furthermore, since the second lead 15 includes the neck portion17, the second lead 15 contacts the encapsulation resin over anincreased contact area even if a stress is applied on the leads 14 to16, thereby causing stripping at the interface between the leads 14 to16 and the encapsulation resin during or after the manufacture of aresin-encapsulated semiconductor device using the lead frame. Therefore,it is possible to reduce the thermal stress and the mechanical stress,and to stop the progress of the stripping. In order for the stripping toprogress past the neck portion 17, a greater stress is required sincethe width of the second lead 15 increases from the neck portion 17.Therefore, the stripping is suppressed from progressing inward past theneck portion 17. Thus, by providing the neck portion 17 in the secondlead 15, it is possible to realize a resin-encapsulated semiconductordevice resistant to stripping.

[0068] Furthermore, since the stepped portions 14 c to 16 c are formedaround the bonding pads 14 a to 16 a, which are provided on the uppersurfaces of the leads 14 to 16, respectively, the stepped portions 14 cto 16 c function to stop the progress of the stripping at the interfacebetween the leads 14 to 16 and the encapsulation resin. Therefore, thestepped portions 14 c to 16 c, together with the neck portion 17 of thesecond lead 15, provide a synergistic effect of stopping the progress ofthe stripping between the encapsulation resin and the leads.

Resin-encapsulated Semiconductor Device

[0069] Next, a resin-encapsulated semiconductor device using the leadframe of the present embodiment will be described.

[0070]FIG. 4A to FIG. 4C are a top view, a cross-sectional view takenalong line IV-IV and a bottom view, respectively, illustrating theresin-encapsulated semiconductor device of the present embodiment. InFIG. 4A, components that are encapsulated in an encapsulation resin areillustrated by broken lines.

[0071] As illustrated in FIG. 4A to FIG. 4C, the resin-encapsulatedsemiconductor device of the present embodiment includes the rectangulardie pad 12, the suspension leads 13 for supporting the die pad 12, asemiconductor chip 20 mounted on the die pad 12 with the lower surfacethereof being bonded on the upper surface of the die pad 12 via anadhesive, a group of leads including the first to third leads 14 to 16each extending toward the corresponding side of the die pad 12, thinmetal wires 21 electrically connecting electrodes of the semiconductorchip 20 with the bonding pads 14 a to 16 a of the leads 14 to 16 amongthe group of leads, and an encapsulation resin 22 encapsulating thesemiconductor chip 20, the leads 14 to 16, the thin metal wires 21, thesuspension leads 13 and the die pad 12 together on the upper side of thelead frame. Note however that the reverse surface of the die pad 12, thelands 14 b to 16 b on the reverse surface of the leads 14 to 16, and theouter side surface of each of the first and second leads 14 and 15 arenot covered with the encapsulation resin 22 but are exposed on thereverse surface of the package (resin-encapsulated semiconductordevice). The exposed lands 14 b to 16 b of the leads 14 to 16 functionas external terminals.

[0072] The structure of each of the leads 14 to 16 is as described abovein the description of the structure of the lead frame. Specifically, thegroup of leads include at least three kinds of leads, i.e., the first,second and third leads 14, 15 and 16. The first bonding pad 14 a, towhich the thin metal wire 21 is connected, is provided on the uppersurface of each first lead 14, and the first land 14 b, which is exposedon the lower surface of the encapsulation resin 22 and functions as anexternal terminal, is provided on the lower surface of the first lead14. The second bonding pad 15 a, to which the thin metal wire 21 isconnected, is provided on the upper surface of the second lead 15, andthe second land 15 b, which is exposed on the lower surface of theencapsulation resin 22 and functions as an external terminal, isprovided on the lower surface of the second lead 15. The third bondingpad 16 a, to which the thin metal wire 21 is connected, is provided onthe upper surface of the third lead 16, and the third land 16 b, whichis exposed on the lower surface of the encapsulation resin 22 andfunctions as an external terminal, is provided on the lower surface ofthe third lead 16.

[0073] The first lead 14 and the third lead 16 are electrically andphysically separated from each other. Note that even if a portion of thefirst lead 14 and a portion of the third lead 16 are connected to eachother via a very thin line such that the connection has a very highelectric resistance to substantially block signals passing therethrough,it can be said that they are electrically separated from each other. Onthe other hand, in a resin-encapsulated semiconductor device thathandles high frequency signals, it is preferred that the first lead 14and the third lead 16 are separated from each other by a distance suchthat crosstalk does not occur therebetween. While one end of the firstlead 14 is exposed on the side surface of the package (or theencapsulation resin 22), both ends of the third lead 16 are buried inthe encapsulation resin 22 without reaching the side surface of thepackage. By providing a lead that has both ends buried in theencapsulation resin, as does the third lead, it is possible to increasethe number of lands that function as external terminals withoutincreasing the number of leads that reach the side surface of theencapsulation resin, whereby it is possible to easily obtain aresin-encapsulated semiconductor device having three or more rows ofexternal terminals.

[0074] Moreover, the second lead 15 includes the neck portion 17 havinga reduced width in the vicinity of the second land 15 b. The width ofthe neck portion 17 is about 40 μm to 100 μm, for example.

[0075] The first to third bonding pads 14 a to 16 a are protrudingupwardly from the pressed region Rpres having a reduced thickness, withthe stepped portions 14 c to 16 c existing between the pressed regionRpres and the bonding pads 14 a to 16 a.

[0076] Moreover, the first to third lands 14 b to 16 b are provided in aplanar arrangement forming three rows in an area of the lower surface ofthe encapsulation resin 22 (see FIG. 4C). Thus, the resin-encapsulatedsemiconductor device of the present embodiment is an LGA typeresin-encapsulated semiconductor device having three rows of externalterminals.

[0077] The resin-encapsulated semiconductor device of the presentembodiment employs the lead frame described above, and thereforeprovides the following effects as already described above.

[0078] First, the first and third leads 14 and 16, which are connectedto each other when the lead frame is produced, are separated from eachother in a subsequent step, whereby a number of rows of lands can easilybe provided without reducing the dimension between leads that are nextto each other. For example, if a lead that is separated into two leadsin a subsequent step is provided instead of the second lead 15, it ispossible to obtain a resin-encapsulated semiconductor device having fourrows of external terminals.

[0079] Furthermore, the second lead 15 includes the neck portion 17,whereby the width of the second lead 15 is reduced at the neck portion17. Therefore, the second lead 15 contacts the encapsulation resin overan increased contact area even if a stress is applied on the leads 14 to16, thereby causing stripping at the interface between the leads 14 to16 and the encapsulation resin 22 during or after the manufacture of aresin-encapsulated semiconductor device using the lead frame. Therefore,it is possible to reduce the thermal stress and the mechanical stress,and to stop the progress of the stripping. In order for the stripping toprogress past the neck portion 17, a greater stress is required sincethe width of the second lead 15 increases from the neck portion 17.Therefore, the stripping is suppressed from progressing inward past theneck portion 17. Thus, by providing the neck portion 17 in the secondlead 15, it is possible to realize a resin-encapsulated semiconductordevice resistant to stripping.

[0080] Furthermore, since the stepped portions 14 c to 16 c are formedaround the bonding pads 14 a to 16 a, which are provided on the uppersurfaces of the leads 14 to 16, respectively, the stepped portions 14 cto 16 c function to stop the progress of the stripping at the interfacebetween the leads 14 to 16 and the encapsulation resin 22. Therefore,the stepped portions 14 c to 16 c, together with the neck portion 17 ofthe second lead 15, provide a synergistic effect of stopping theprogress of the stripping between the encapsulation resin and the leads.

[0081] Next, a method for manufacturing the resin-encapsulatedsemiconductor device of the present embodiment will be described withreference to FIGS. 5A and 5B to FIGS. 10A and 10B.

[0082]FIGS. 5A and 5B are a plan view and a cross-sectional view takenalong line V-V, respectively, illustrating the step of preparing a leadframe. First, in the step of FIGS. 5A and 5B, a lead frame is prepared.Specifically, a lead frame to be prepared in this step includes theframe body 11 (outer frame) made of a metal plate that contains copper(Cu) as its main component, the die pad 12 placed in an opening of thelead frame for mounting a semiconductor chip thereon, the suspensionleads 13 each having one end supporting a corner of the die pad 12 andthe other end connected to the frame body 11, and a group of leads eachhaving a tip portion extending toward the corresponding side of the diepad 12 and a base portion connected to the frame body 11. The firstbonding pad 14 a is provided on the upper surface of the first lead 14,among the group of leads, and the first land 14 b, opposing the firstbonding pad 14 a, is provided on the lower surface of the first lead 14.The second bonding pad 15 a is provided on the upper surface of thesecond lead 15, among the group of leads, and the second land 15 b,opposing the second bonding pad 15 a, is provided on the lower surfaceof the second lead 15. The third bonding pad 16 a is provided on theupper surface of the third lead 16, among the group of leads, and thethird land 16 b, opposing the third bonding pad 16 a, is provided on thelower surface of the third lead 16.

[0083] Moreover, a region of each of the leads 14, 15 and 16 excludingthe bonding pads 14 a, 15 a and 16 a and the lands 14 b, 15 b and 16 bis a pressed region Rpres whose thickness is reduced through a pressingprocess. The bonding pads 14 a, 15 a and 16 a respectively include thestepped portions 14 c, 15 c and 16 c protruding upwardly from the pressregions Rpres having a reduced thickness.

[0084] While the first lead 14 and the third lead 16 are connected toeach other upon production of the lead frame, the thickness of theconnecting portion Rcnct therebetween is reduced so that the first lead14 and the third lead 16 can be separated from each other in asubsequent step.

[0085] Although FIG. 5A and FIG. 5B only show, as a unit, a region ofthe lead frame on which one semiconductor chip is mounted, the entirelead frame actually includes a plurality of such units as illustrated inFIG. 5A and FIG. 5B that are arranged next to each other in a matrixpattern.

[0086]FIG. 6A and FIG. 6B are a plan view and a cross-sectional viewtaken along line VI-VI, respectively, illustrating the step of cutting aconnecting portion between the first and third leads 14 and 16. In thestep illustrated in FIG. 6A and FIG. 6B, an encapsulation sheet 30 isattached to the lower surface of the lead frame, and each connectingportion Rcnct between the first lead 14 and the third lead 16 is punchedthrough using a punch 31 in each opening of the lead frame, therebyelectrically separating the first and third leads 14 and 16 from eachother. The encapsulation sheet 30 may be made of a polyimide resin andan adhesive, and has a thickness of about 5 μm to about 100 μm.

[0087]FIG. 7A and FIG. 7B are a plan view and a cross-sectional viewtaken along line VII-VII, respectively, illustrating the die bondingstep. In the step illustrated in FIG. 7A and FIG. 7B, the upper surfaceof the protruding portion of the die pad 12 and the lower surface of thesemiconductor chip 20 are bonded together via an adhesive while the leadframe is attached to the encapsulation sheet 30, thus mounting thesemiconductor chip 20 on the die pad 12.

[0088] Since the protruding portion 19 is provided in the die pad 12,there is a gap between the lower surface of the semiconductor chip 20and the die pad 12 beside the protruding portion 19.

[0089]FIGS. 8A and 8B are a plan view and a cross-sectional view takenalong line VIII-VIII, respectively, illustrating the wire bonding step.In the step of FIGS. 8A and 8B, electrodes of the semiconductor chip 20,which has been mounted on the die pad 12, are electrically connected tothe first to third bonding pads 14 a to 16 a of the lead frame via thethin metal wires 21 while the lead frame is attached to theencapsulation sheet 30.

[0090]FIGS. 9A and 9B are a plan view and a cross-sectional view takenalong line IX-IX, respectively, illustrating the resin encapsulationstep. In the step of FIGS. 9A and 9B, the entire area of the uppersurface of the lead frame is encapsulated by the encapsulation resin 22in a single process while the lead frame is attached to theencapsulation sheet 30. In FIG. 9A, components that are encapsulated inthe encapsulation resin 22 are illustrated by broken lines. Moreover, inFIGS. 9A and 9B, each cut line (dicing line) along which the lead frameis cut into individual resin-encapsulated semiconductor devices(packages) in a subsequent step is illustrated by a one-dot chain line.

[0091]FIGS. 10A and 10B are a plan view and a cross-sectional view takenalong line X-X, respectively, illustrating the dicing step. In the stepof FIGS. 10A and 10B, the encapsulation sheet 30 attached to the lowersurface of the lead frame is removed, and then the lead frame is cut bya rotating blade into individual resin-encapsulated semiconductordevices 23. In this process, the lead frame is cut along a line that isslightly inner than the connecting portion at which the first and secondleads 14 and 15 and the suspension leads 13 of the lead frame areconnected to the frame body 11 (see FIGS. 4A and 4B).

[0092] The method for manufacturing the resin-encapsulated semiconductordevice of the present embodiment provides the following advantages. Thesecond lead 15 of the lead frame includes the neck portion 17, wherebythe width of the second lead 15 is reduced at the neck portion 17.Therefore, the second lead 15 contacts the encapsulation resin over anincreased contact area even if a stress is applied on the leads 14 to16, thereby causing stripping at the interface between the leads 14 to16 and the encapsulation resin 22 during the manufacture of aresin-encapsulated semiconductor device using the lead frame(particularly, when the lead frame is cut by a rotating blade).Therefore, it is possible to reduce the thermal stress and themechanical stress, and to stop the progress of the stripping. In orderfor the stripping to progress past the neck portion 17, a greater stressis required since the width of the second lead 15 increases from theneck portion 17. Therefore, by providing a neck portion at least in onelead (or leads of one kind) extending from the side surface of thepackage, the stripping can be suppressed from progressing past the neckportion. While a narrow neck portion is provided only in the second lead15 in the present embodiment, the narrow neck portion may alternativelybe provided also in the first lead 14, which is connected to the sidesurface of the package.

[0093] Furthermore, since the stepped portions 14 c to 16 c are formedaround the bonding pads 14 a to 16 a, which are provided on the uppersurfaces of the leads 14 to 16, respectively, the stepped portions 14 cto 16 c function to stop the progress of the stripping at the interfacebetween the leads 14 to 16 and the encapsulation resin 22. Therefore,the stepped portions 14 c to 16 c, together with the neck portion 17 ofthe second lead 15, provide a synergistic effect of stopping theprogress of the stripping between the encapsulation resin and the leads.

[0094] Thus, with the lead frame of the present embodiment, theresin-encapsulated semiconductor device using the same and the methodfor manufacturing the same, since the neck portion 17 having a reducedwidth is provided in the second lead 15 of the lead frame, it ispossible to stop the progress of the stripping between the leads and theencapsulation resin occurring due to a stress applied to the leads inthe shaping/dicing step after resin encapsulation, and to realize aresin-encapsulated semiconductor device having a high reliability.

[0095] Moreover, since the first and third leads 14 and 16, which areconnected to each other when the lead frame is produced, are separatedfrom each other in a subsequent step, it is possible to easily providethree or more rows of external terminals without increasing the numberof leads to be connected to the periphery of the opening of the leadframe.

[0096] Therefore, while the present embodiment has been described abovewith respect to a resin-encapsulated semiconductor device in which threerows of external terminals are provided, it is possible to easilyproduce a resin-encapsulated semiconductor device having four or morerows of external terminals by punching through each of connectingportions connecting together a plurality of sections, which are providedin the form of a single piece upon production of the lead frame, using apunch on an encapsulation sheet as in the above-described embodiment,for example.

[0097] In a case where a resin-encapsulated semiconductor device havingfour or more rows of external terminals is manufactured by a method thatincludes the step (such as the dicing step) of cutting the leadstogether with the encapsulation resin using a rotating blade so as todivide the lead frame into individual resin-encapsulated semiconductordevices (packages), stripping is likely to occur between the leads andthe encapsulation resin during the dicing step. However, by providing aneck portion having a reduced width (such as the neck portion 17 of thesecond lead 15) in at least one lead, the progress of the stripping canbe suppressed, and it is possible to realize an LGA typeresin-encapsulated semiconductor device having a high reliability.

[0098] Alternatively, in the lead frame illustrated in FIG. 1, someleads among the second and third leads 15 and 16 may be connected to thedie pad 12, so that portions connected to the die pad 12 are punchedthrough in the step of punching through each connecting portion Rcnctbetween the first and third leads using a punch. In such a case, even ifthe suspension leads 13 are not provided, the die pad 12 may beconnected to the frame body 11 upon production of the lead frame, sothat the die pad 12 and the leads 15 or 16 can be separated from eachother in a subsequent step.

What is claimed is:
 1. A lead frame, comprising: a frame body made of aconductive material and including at least one opening for mounting asemiconductor chip; a die pad placed in the opening of the frame body;and a group of leads extending from the frame body into the opening, thegroup of leads including at least: a first lead connected to the framebody and including a first bonding pad provided on an upper surface ofthe first lead and a first land provided on a lower surface of the firstlead; a second lead connected to the frame body and including a secondbonding pad provided on an upper surface of the second lead and a secondland provided on a lower surface of the second lead; and a third leadconnected to the first lead and including a third bonding pad providedon an upper surface of the third lead and a third land provided on alower surface of the third lead, wherein a connecting portion that isthinner than the lead frame body and that can be punched through isprovided between the first lead and the third lead.
 2. The lead frame ofclaim 1, wherein at least the second lead includes a neck portion havinga smaller width than other portions as viewed in a plan view.
 3. Thelead frame of claim 1, wherein each lead includes a region around thebonding pad thereof that has a smaller thickness than that of a portionof the lead corresponding to the bonding pad, with a stepped portionbeing provided between the bonding pad and the region around the bondingpad.
 4. The lead frame of claim 1, wherein the first, second and thirdlands are substantially coplanar on a common plane while being arrangedin three rows on the common plane.
 5. The lead frame of claim 1, whereinthe second lead and a lead structure including the first and third leadsare arranged alternately along a periphery of the opening of the framebody.
 6. The lead frame of claim 1, wherein the frame body, the die padand the group of leads are made of a single metal plate.